CN116457893A - Nuclear reactor module and nuclear district heating reactor comprising the same and method of operating the same - Google Patents

Abstract

According to an exemplary aspect of the invention, a nuclear reactor module is provided having a containment vessel (200) and a reactor pressure vessel (300) contained within the containment vessel (200). The reactor pressure shell (300) includes a primary circuit (320, 440) having a primary fluid (450) and a reactor core (500) cooled by the primary fluid (450). An intermediate volume (210) is formed between the containment vessel (200) and the reactor pressure vessel (300). The intermediate volume (210) is partially filled with an intermediate fluid (220). The circulation of the primary fluid (450) is permanently separated from the intermediate volume (210).

Description

Nuclear reactor module and nuclear district heating reactor comprising the same and method of operating the same

Technical Field

The present invention relates to nuclear power. In particular, the invention relates to passive removal of decay heat after reactor shutdown.

Background

Nuclear safety relies on certain basic principles such as the coolability of nuclear fuel and the principles of deep defence. The former means that sufficient coolant flow is maintained in the reactor core to avoid structural damage caused by overheating. This requirement covers both normal and transient operating conditions when the reactor is producing fission energy, as well as all conditions when the reactor is shutdown but radioactive decay (decay heat) produces a significant amount of waste heat. The coolant flow may be maintained by a forced circulation based active system or by a passive system relying on natural convection. The current trend in reactor design is to replace the electric pumps with passive systems that do not require active measures to drive or maintain coolant flow. The principle of deep defense is based on the requirement that the radioisotope in the nuclear fuel be isolated from the environment by a plurality of successive and independent barriers. The two outermost barriers associated with this application are the primary circuit (in this case the reactor pressure shell) and the containment vessel (in this case the containment vessel). The large amount of radioactive emissions would require the fuel to be subjected to considerable damage and all the successive release barriers would be broken.

An passive device for passive cooling and decay heat removal is proposed in US 2010/012333 A1. US 2010/012383 A1 discloses a reactor core contained in a pressurized reactor pressure vessel that is contained in an internally dry containment vessel, which in turn is submerged in a pool of water. The dry space between the reactor and the containment acts as thermal insulation so that the reactor can operate at high temperatures without significant heat loss. The reactor module has an emergency cooling system that is activated by opening two sets of valves in the reactor pressure shell. The containment space is filled with water, disrupting the thermal insulation and effecting natural circulation that transfers heat from the reactor core to the surrounding pool of water (i.e., the final radiator).

However, there remains a need to further improve the reliability of passive devices for removing decay heat from nuclear reactors relying on mechanical elements that may introduce points of failure when they fail.

Disclosure of Invention

The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

According to a first aspect of the present disclosure, a nuclear reactor module is provided having a containment vessel and a reactor pressure vessel contained within the containment vessel. The reactor pressure shell contains a primary circuit with a primary fluid and a reactor core cooled by the primary fluid. An intermediate volume is formed between the containment and reactor pressure shells. The intermediate volume is partially filled with an intermediate fluid. The intermediate fluid may be a liquid, such as water. The circulation of the primary fluid is permanently separated from the intermediate volume.

According to a second aspect of the present invention, there is provided a nuclear district heating reactor having such a nuclear reactor module.

According to a third aspect of the invention, a method of operating such a nuclear reactor module is provided.

Various embodiments of the first aspect may include at least one feature listed item-by-item as follows:

-the reactor pressure shell is configured to prevent all fluid flow between the reactor pressure shell and the containment shell;

-the reactor pressure shell is made of a thermally conductive material;

-the temperature of the primary fluid at the downcomer is lower than the boiling point of the intermediate fluid;

-in normal operating mode of the nuclear reactor module, the temperature of the primary fluid is lower than the boiling point of the intermediate fluid;

-the reactor pressure shell is pressurized to an overpressure;

-an overpressure between 5 and 10 bar;

-the nuclear reactor module is configured to operate in a normal operating mode and in an passive decay heat removal mode;

-in normal operation mode, the temperature of the primary fluid at the downcomer is lower than the boiling point of the intermediate fluid;

-in normal operation mode, the temperature of the intermediate fluid is lower than the boiling point of the intermediate fluid;

-in the passive decay heat removal mode, the temperature of the primary fluid at the downcomer is at or above the boiling point of the intermediate fluid;

-in the passive decay heat removal mode, the temperature of the intermediate fluid is at the boiling point of the intermediate fluid;

-forming a heat conducting channel between the nuclear reactor core and the environment or radiator when the intermediate fluid boils;

-in passive decay heat removal mode, the containment wall temperature is maintained below the intermediate fluid boiling point to facilitate efficient heat transfer;

boiling in the reactor pressure shell wall region via the intermediate fluid and condensing into the containment wall region for efficient heat transfer;

-a primary heat transfer mechanism that excludes decay heat from the reactor core in an inactive decay heat removal mode;

passive removal of decay heat independent of forced circulation of primary or secondary fluid, or actuation of mechanical components;

-the primary fluid is water;

-the intermediate fluid is water;

-core outlet temperature between 120-150 ℃;

-the temperature of the primary fluid at the downcomer is lower than 100 ℃;

the nuclear reactor module comprises a passive decay heat removal system provided by a heat conducting channel between the reactor core and the surrounding environment or radiator when the intermediate fluid reaches its boiling point;

-the reactor pressure shell does not comprise thermal insulation;

the primary circuit comprising a riser, a downcomer cooperatively associated with the riser, and a primary fluid,

the containment vessel is placed in a heat sink,

the radiator is a pool of water and,

the containment vessel is pressurized to an overpressure for increasing the boiling point of the intermediate fluid.

Numerous benefits can be obtained with the present invention. The transition from normal operation to passive decay heat removal mode occurs naturally when the primary heat transfer path from the primary loop is compromised and the temperature of the primary fluid at the heat exchanger outlet is raised sufficiently to cause boiling of the intermediate fluid. The established heat transfer path from the reactor core to the final radiator is independent of the function of the valves or any other mechanical components. Heat transfer from the primary fluid to the intermediate fluid is accomplished by conduction through the reactor pressure shell and walls. The two volumes are permanently separated without breaking any release barrier required to reasonably apply the principles of deep defenses. The invention thus greatly improves the robustness of the decay heat removal device for a double-shell reactor operating at low temperatures.

Drawings

Certain embodiments of the present invention are described in more detail below with reference to the accompanying drawings, wherein FIG. 1 shows a schematic cross-sectional view of a nuclear district heating reactor in accordance with at least some embodiments of the present invention.

Detailed Description

In the present context, the expression "permanently separated" means, but is not limited to, that the circulation of the primary fluid is permanently separated from the intermediate volume. This applies to all normal and expected operating events and accidents, but with the exception of the case of opening an overpressure valve to prevent catastrophic structural failure of the reactor pressure shell.

In the present context, the expression "passive decay heat removal" refers to a heat removal system that does not rely on signal input, external power or external forces, or moving mechanical parts, but relies on moving working fluid. In other words, the inactivity level corresponds to "class B inactivity" (IAEA-TECDOC-626, ISSN 1011-4289, available on-line to https:// www-pub. IAEA. Org/MTCD/publications/PDF/te_626_web. PDF) as understood in the art and as described in "Safety related terms for advanced nuclear plants" published by International atomic energy agency, 1991, 9.

Fig. 1 illustrates a nuclear reactor module in accordance with at least some embodiments of the invention. The module is placed in a chamber 100 containing a pool of water that acts as a heat sink 110 for heat from the module when the normal cooling path is not available. In normal operation, heat generated by the module is transferred through the heat exchanger to an external secondary circuit (not shown). The water in the tank may be at room temperature, for example typically between about 25 ℃ and 40 ℃ at atmospheric pressure. Alternatively, the radiator may be another liquid pool, an air cooled space, or a bed of fluid particles (such as sand or salt).

The module has a containment vessel 200 immersed in a heat sink 110. Containment vessel 200 is preferably completely submerged. Containment 200 is an enclosure for housing reactor pressure shell 300, reactor pressure shell 300 including reactor core 500 and associated heat transfer components. The purpose of the containment vessel 200 is thus to provide an intermediate volume 210 between the radiator 110 and the reactor pressure vessel 300 and to act as one of the barriers to release of radioactive material. Containment vessel 200 has a solid housing for preventing any fluid flow between the interior intermediate volume 210 of containment vessel 200 and a surrounding relatively cool mass (e.g., ambient air or a pool of water, or a sand pit acting as heat sink 110). The housing may have an elongated shape, such as a generally cylindrical shape with rounded ends, for maximizing the load bearing capacity. The housing may be made of metal, such as steel, in particular austenitic steel. The material preferably has good heat conducting properties. However, containment vessel 200 does include sealed outlets and inlets for transferring heat between reactor pressure vessel 300 and external consumers, but these components are omitted from FIG. 1 for simplicity. Furthermore, the containment vessel 200 may be secured or suspended to the chamber 100 by mechanical connection elements, which are omitted from fig. 1 for brevity.

The intermediate volume 210 between the containment vessel 200 and the reactor pressure vessel 300 is partially filled with an intermediate fluid 220. Fig. 1 shows that the intermediate fluid level is quite low. According to an embodiment, the intermediate fluid level is between the top of the reactor core 500 and the heat exchanger 310. The intermediate fluid 220 may be, for example, water. The intermediate fluid 220 may be at or near ambient pressure at a slight overpressure under normal operating conditions. Under normal operating conditions, a portion of the intermediate volume 210 is occupied by the intermediate fluid 220. The amount of intermediate fluid 220 is selected so as to provide a sufficiently large heat transfer area. A typical level of intermediate fluid 220 is below the bottom end of the heat exchanger, which will be discussed later. The boiling point of the intermediate fluid 220 may be about 100 ℃ at about ambient pressure.

Although the reactor pressure vessel 300 and the containment vessel 200 may be made of a thermally conductive material, thermal insulation may be added to the lower portion of the containment vessel 200. According to an embodiment, the containment vessel 200 includes a thermally insulating layer (omitted from the figures) that extends upward from the bottom of the containment vessel 200 to the normal level of the intermediate fluid 220. The thermal insulation layer may extend from the bottom of the containment vessel 200 to between the reactor core 500 and the heat exchanger 310, for example. The thermal insulation layer may be provided on the inner or outer surface of the containment wall, for example by spraying. The purpose of the thermal insulation is to limit the heat flux between the reactor core 500 and the radiator 110 in the normal operating mode.

The reactor pressure vessel 300 is contained within the containment vessel 200 and is secured or suspended to the containment vessel 200 by mechanical connection elements, which are omitted from fig. 1 for the sake of brevity. The reactor pressure shell 300 has a solid housing for preventing any fluid flow between the interior volume of the reactor pressure shell 300 and the intermediate volume 210. The housing may have an elongated shape, such as a generally cylindrical shape with rounded ends, for maximizing the load bearing capacity. The housing may be made of metal, such as steel, in particular austenitic steel. The material preferably has good heat conducting properties.

The reactor pressure vessel 300 contains the components required to sustain a fission chain reaction to generate heat, particularly for district heating systems. The basic structure of the reactor pressure shell 300 is relatively conventional for an integrated pressurized water reactor. A preferred application of the invention is a nuclear district heating reactor operating at relatively low temperatures. The reactor pressure shell 300 is pressurized to several bars, for example 5 bars. The reactor pressure shell 300 also contains a primary fluid 450. The primary fluid 450 may be, for example, water. The boiling point of primary fluid 450 is dependent on pressure. The operating temperature is limited by the temperature of primary fluid 450 at downcomer 440 (i.e., after heat exchanger 310), which remains below the boiling point of intermediate fluid 220 in the normal operating mode.

The reactor pressure shell 300 accommodates a reactor core 500 placed at the bottom of the reactor pressure shell 300. The reactor core 500 may be a light water reactor core. The core may be fueled by uranium oxide particles contained in zirconium-based metal tubes. Of course, other fuels are also contemplated. A core basket 400, also disposed within the reactor pressure shell 300, encloses the reactor core 500 and associated components, including the primary loop. A primary loop is associated with the reactor core 500 for extracting heat generated by the reactor core 500 and providing it to an external secondary loop (not shown). The primary loop has a riser 320 for hot water heated by the reactor core 500, a downcomer 440 surrounding the riser 320 for returning water to the reactor core 500, a heat exchanger 310 positioned in the downcomer 440 for absorbing heat, and a primary fluid 450 contained in the reactor pressure shell 300 for transferring heat between the reactor core 500 and the heat exchanger 400.

The core basket 400 has a perforated floor for suspending the reactor core 500 in flow communication with the primary fluid 450. In other words, the reactor core 500 is immersed in the primary fluid 450. The reactor core 500 is held in place by a top mounted support plate 410, which support plate 410 supports guide tubes 430 for the control assembly. A reflector 420 is disposed around the reactor core 500 inside the core basket 400 for improving neutron performance of the reactor core and reducing radiation load to the containment wall. The lift tubes 320 form channels for upward coolant flow above the reactor core 500. The heat exchanger 310 is installed in a space, particularly an annular space, between the lift tube 320 and the reactor pressure shell 300 so as to be impacted by the primary fluid 450 circulated in the reactor pressure shell 300 through heating and cooling cycles of the primary fluid 450. This space forms a downcomer 440 for cooling fluid returned to the bottom chamber of the reactor pressure shell 200. The heat exchanger 310 may be a water-to-water heat exchanger having a pilot tube (not shown in fig. 1) penetrating the containment vessel for fluid communication with an external secondary circuit including the consumer, such as a heat exchanger-to-tertiary circuit, for example a district heating circuit (not shown in fig. 1). The control rod drive mechanism 600 is mounted on the top module, in particular to the top of the intermediate volume 210, and is connected to the control rods via shafts that extend through guide tubes 430, the guide tubes 430 passing through sealed tubing provided to the reactor pressure shell 200.

The reactor primary loop is completely enclosed within the reactor pressure shell 300. The primary fluid 450 is heated in the reactor core 500. This flow is directed upwardly within a lift tube 320 located in the central portion of the reactor pressure shell. The liquid stream is then diverted to flow downwardly through heat exchanger 310 where energy is transferred to the secondary side (omitted from the figure). The coolant exits the heat exchanger from the bottom, flows through downcomer 440, and then reenters the reactor core. The circulation may be forced, i.e. maintained by a pump, or based on natural convection, as shown in fig. 1. The coolant temperature at the downcomer and core inlet is less than 100 ℃. The temperature at the core outlet is about 120-150 ℃.

As described above, the reactor modules operate at relatively low temperatures. In the normal mode of operation, the temperature of the primary fluid 450 at the lift tube 320 is in the range of 120-150 ℃ at about 5-10 bar. In the normal mode of operation, when water is used as intermediate fluid 220, the temperature of primary fluid 450 at downcomer 440 (i.e., after passing through heat exchanger 310) is less than 100 ℃. More specifically, the temperature of primary fluid 450 at downcomer 440 is below the boiling point of intermediate fluid 220. In other words, the temperature of the primary fluid at the outlet of heat exchanger 310 increases sufficiently to cause boiling of intermediate fluid 220.

If the normal heat transfer path through the heat exchanger is compromised, heat generated in the reactor core 500 is trapped within the reactor pressure shell 200. The reactor module itself will then switch to the passive decay heat removal mode without external input. The temperature of the primary fluid 450 increases. Heat is conducted through the walls of the reactor pressure shell 200 causing the intermediate fluid 220 to warm. Eventually the intermediate fluid 220 begins to boil, creating a very efficient heat transfer path between the reactor core 500 and the radiator 110. The thermally conductive properties of the containment vessel 200 further facilitate the conduction of heat through the containment vessel 200 to the heat sink 110. The heat capacity of the radiator 110 is designed to be large enough to withstand the heat that the reactor may generate during an emergency shutdown, which may take weeks. The transition to normal operating mode may also be made without any intervention, in which case the reactor core 500 may be started or the process may continue once the temperatures of the primary fluid 450, intermediate fluid 220, and the radiator 110 are restored to acceptable levels.

According to a further embodiment, the containment vessel 200 is pressurized to an overpressure. By increasing the pressure of the intermediate volume 210, the boiling point of the intermediate fluid 220 is also increased. For example, if water is used as the intermediate fluid 220, the boiling point of the intermediate fluid 220 may exceed 100 ℃, such as 110 ℃. The overpressure may be up to 5 bar. The magnitude of the overpressure is selected such that the boiling point of the intermediate fluid 220 is lower than the boiling point of the primary fluid 450.

It is to be understood that the disclosed embodiments of the invention are not limited to the specific structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as recognized by those of ordinary skill in the relevant arts. It is also to be understood that the terminology employed herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment.

As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, individual members of such a list should not be construed as actual equivalents of any other member of the same list solely based on their presentation in the same group without reverse presentation. Furthermore, various embodiments and examples of the invention may be mentioned together with alternatives to the various components thereof. It is understood that such embodiments, examples and alternatives are not to be construed as actual equivalents of each other, but are to be considered as separate and autonomous representations of the invention.

Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

While the foregoing embodiments illustrate the principles of the invention in one or more specific applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, use and implementation details can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

The verbs "comprise" and "comprise" are used in this document as open-ended limits that neither exclude nor require the presence of additional unrecited features. The features recited in the dependent claims are freely combinable with each other unless explicitly stated otherwise. Furthermore, it should be understood that the use of "a" or "an" (i.e., in the singular) throughout this document does not exclude a plurality.

List of reference numerals

List of references

Patent literature

US 2010/0124303 A1

Non-patent literature

International atomic energy organization, "Safety related terms for advanced nuclear plants" (IAEA-TECDOC-626, 9 th 1991, ISSN 1011-4289, available on-line to https:// www-pub. IAEA. Org/MTCD/publications/PDF/te_626_web. PDF).

Claims (11)

1. A nuclear reactor module, comprising:

a containment vessel (200);

a reactor pressure shell (300) contained in the containment shell (200), the reactor pressure shell (300) comprising a primary circuit (320, 440) having a primary fluid (450); and

a reactor core (500) contained in the reactor pressure shell (300) and cooled by the primary fluid (450),

wherein an intermediate volume (210) is formed between the containment vessel (200) and the reactor pressure vessel (300), the intermediate volume (210) being partially filled with an intermediate fluid (220), the intermediate fluid being water,

characterized in that the circulation of the primary fluid (450) is permanently separated from the intermediate volume (210).

2. The nuclear reactor module of claim 1 wherein the reactor pressure shell (330) is configured to prevent all fluid flow between the reactor pressure shell (330) and the containment shell (200).

3. The nuclear reactor module according to any one of the preceding claims wherein the reactor pressure shell (330) is made of steel, preferably austenitic steel.

4. The nuclear reactor module according to any one of the preceding claims wherein passive removal of decay heat is independent of forced circulation of the primary fluid (450) or driven mechanical components, such as valves.

5. The nuclear reactor module according to any one of the preceding claims wherein the primary fluid (450) is water.

6. The nuclear reactor module according to any one of the preceding claims, wherein the nuclear reactor module comprises an passive decay heat removal system provided by a thermally conductive channel between the reactor core (500) and the surrounding environment or radiator (110) when the intermediate fluid (220) reaches its boiling point.

7. A nuclear district heating reactor, characterized by a nuclear reactor module according to any one of the preceding claims 1 to 6.

8. A method of operating a nuclear reactor module according to any one of the preceding claims 1 to 6, the method comprising maintaining the circulation of the primary fluid (450) separate from the intermediate volume (210).

9. The method of claim 8, wherein the nuclear reactor module operates in two modes, namely:

a normal operation mode in which the temperature of the primary fluid (450) after passing through the heat exchanger (310) is such that the temperature of the intermediate fluid (220) heated by conduction through the reactor pressure shell wall (300) is lower than the boiling point of the intermediate fluid (220), an

An passive decay heat removal mode in which:

the primary fluid (450) having a temperature at or above the boiling point of the intermediate fluid (220) after passing through the heat exchanger (310), and

the temperature of the intermediate fluid (220) is at the boiling point of the intermediate fluid (220),

wherein the hot primary fluid (450) and the boiling intermediate fluid (220) form a thermally conductive path between the nuclear reactor core (500) and an environment or radiator (110).

10. The method of claim 9, comprising: in the passive decay heat removal mode, the walls of the containment vessel (200) are cooled to a temperature below the boiling point of the intermediate fluid (220) for facilitating efficient heat transfer via the intermediate fluid (220) boiling at the reactor pressure vessel wall (300) and condensing to the containment vessel wall (200), which is the primary heat transfer mechanism that removes decay heat from the reactor core (500).

11. The method of claim 9 or 10, wherein the core (500) outlet temperature is 120-150 ℃.